Aluminum-doped zinc oxide (AZO) is one of the most promising alternatives to replace the most commonly used indium tin oxide (ITO). Indeed, comparable electrical and optical performances have been demonstrated and the material cost is lower.
Reducing production cost is becoming a critical issue considering the ever-increasing demand for flat-panel displays, solar cells and smart windows.
Wet-chemistry represents a low cost alternative production technology compared to traditional techniques such as sputtering or evaporation, and NCs have the advantage over sol-gel methods that they are already crystalline before film deposition, reducing the thermal budget required for annealing.29′30
Aluminum-doped zinc oxide (AZO), with its comparable optical and electronic properties, represents a lower cost, less toxic, earth abundant alternative to the widely used transparent conducting oxide (TCO), indium tin oxide (ITO).1 At the same time, TCO nanocrystals (NCs) have recently gained interest owing both to the low cost of solution processing and the potential to exploit size-dependent properties.2-8 Deposition of colloidal TCO NCs as a nanoink is highly appealing for integration into emerging flexible electronics, such as displays, electronic paper or solar cells.9 Moreover, their significantly higher surface area than conventionally deposited TCO thin films could enable improvements in devices like electrochromic windows and dye-sensitized solar cells, as well as biosensors.10 
While the synthesis of ITO colloidal NCs has recently advanced markedly, it remains still a challenge to control dopant incorporation along with size, shape and solvent dispersability in zinc oxide based TCO NCs, i.e. aluminum doped zinc oxide (AZO), indium-doped zinc oxide (IZO) or gallium-doped zinc oxide (GZO).2-8 
Only when the dopants occupy substitutional sites in the interior of the particles are free carriers introduced and the desired electrical and optical properties achieved.11-14 Carefully balancing crystal growth and dopant incorporation rates is thus obligatory.